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In 2009, television broadcasting stations in the United States began broadcasting digital television (DTV) signals after federal mandate. The DTV standards of transmission are set by a non-profit organization, the Advanced Television Systems Committee (ATSC). High-definition television (HDTV) resolutions are significantly higher than those of standard definition, and ATSC HDTV is high-definition television that follows the standards set forth by the ATSC. Likewise, television sets capable of accepting ATSC HDTV signals can be referred to as ATSC HDTV sets. ATSC HDTV can, therefore, refer to both the ATSC standards as well as the associated hardware.
The standard high-definition television resolutions fall into three categories: 720p, 1080p, and 1080i, where 1080p is often referred to as true or full high-definition (HD). These resolutions refer to the frame size of the image, where the number represents the number of vertical pixels in the image. In 720p, the actual resolution – horizontal x vertical – is 1280 x 720; in the 1080 resolutions, the frame size is 1920 x 1080. The letters designated in the resolutions refer to the method of image scanning, P indicating progressive scan and I denoting the scan as interlaced.
ATSC standards call for a variety of DTV screen resolutions and picture aspect ratios, including standard definition (SD) broadcast in 480i/p and 576i/p with aspect ratios of 4:3 and 16:9. For ATSC HDTV, screen resolutions are defined under the three standard HD image sizes and scanning modes, and all HD broadcasts are in the 16:9 widescreen aspect ratio. Image frame rates, given in hertz (Hz), cover a broad range for HD signals. Frame rates for 720p range from 23.976 Hz up to 60 Hz, 1080i ranges from 25 Hz to 30 Hz, and 1080p from 23.976 Hz to 30 Hz.
For video signal transport, ATSC uses the moving picture experts group (MPEG) transport stream and the MPEG-2 codec. Once the signal reaches its endpoint, before the video and audio can be transmitted to the end user, several actions must take place. Among other things, the signal must be decompressed, demodulated, and error corrected. All of these actions require an ATSC tuner; ATSC HDTV sets have an integrated ATSC tuner, negating the need for external hardware. The switch to DTV in 2009 forced many consumers without ATSC HDTV or a separate piece of hardware with integrated ATSC to purchase an external converter box; but as of 2007, all television sets and interfacing devices manufactured are required to feature an integrated ATSC tuner.